Variable inductance device



Nov. 16, y1943.

A o. DODGE VARIABLE INDCTANCE DEVICE FiledOct. 29, 1941 HANG( 0f 0V/,Blf 0R TlM//A/ ELEMENT, ON LINEAR SCALE Inventor-z Alber-t, O. Dodge,

His Attorneg.

Patented Nov. 16,1943

VARIABLE INDUCTAN CE DEVICE Albert 0. Dodge, Schenectady, N. Y., assigner to General Electric Company, a corporation of New York Application October 29, 1941, Serial No. 417,026

6 Claims.

My invention relates to variable inductance devices and particularly to such devices employed as variable controlling means for tuning radio or like circuits over bands of frequencies.

The general object of the invention is to provide compensating means for variable inductance devices such that linear or substantially linear variation of the frequency of a tuned circuit is provided over a considerably extended portion of the range of linear variation of ,a controlling element or elements of the device. This compensation can be extended until linear or substantially linear variation of the inductance of the device results.

It is a particular object to compensate variable inductance tuning devices in such manner that the frequencies of a given band over which a controlled circuit is tuned are distributed more evenly over the range of linear motion of the controlling element or elements of the device, this distribution being preferably substantially linear over an extended frequency range, or in some cases varying from linearity only within predetermined small limits over this extended range.

It is well known that in certain cases it isdesirable to employ a variable inductance instead of a variable capacity in tuning a frequency determining circuit. In accordance with one usual variable inductance tuning method heretofore suggested" the circuit tuning is accomplished by the variation of the mutual inductance between two solenoidal windings; obtained by varying the relative position of the windings with respect to In accordance with the present invention theV above-noted disadvantage is overcome by the provision of a variable inductance device including a combination of windings, certain of which are of opposite inductive sense, so located and proportioned as to compensate for the region or regions of excess change inslope of the characteristic curve.

The novel features which are considered to be 'characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing .wherein Fig. l lil; a diagrammatic representation of a combination of solenoidal windings comprised in a variable inductance device embodying my invention, Fig. 2 is a sectional view of the variable inductance device illustrated diagrammatically in Fig. l, and Fig. 3 shows characteristic curves of inductance and frequency illustrating the invention.

In the variable inductance arrangement illustrated diagrammatically in Fig-1, three windings 1, 2 and 3 are provided connected preferably in series. Two of, the windings, as I and 2, are mounted closely adjacent to each other and movable with respect to each other for varying. their mutual inductance, substantially as in the above-mentioned usual variable inductance tuning method heretofore suggested, and

the third winding, 2, is fixed in position relative to one of the other windings, for example to winding I.

In the sectional view, Fig. 2 o1' the inductance device, the three windings are shown as coaxially disposed, the windings I and 3 being spaced apart and mounted upon a common form or support,v as insulating cylinder 4, at opposite ends thereof, and the winding 2 being mounted upon a similar insulating form or support, as cylinder Il. Windings I and 2 are arranged concentrically and are preferably respectively of such diameter that one winding, as 2, mounted upon its insulating cylinder 5, is disposed within and closely adjacent to the `other winding.

The pair of spaced windings I and3, mounted upon their common support l, and the winding 2 vmounted upon its support 5, are thus movable axially relative to each other from a first position, for example a position .wherein windings I and 2 are closely adjacent to each other throughout their length or a major portiony thereof, to a second position wherein none of winding\I"-or.only a limited' portion thereof is closely adjacent to any portion of winding 2. In the tirst position the winding 2, is at its maximum dista'nce from winding I andfin-the second position the'distance between windings `2..an ci' 3 becomes a minimum.

Windings I and 2 are so connected and wound that their magnetic fields are in the samey direction, as indicated in dotted lines in Fig. 2. Winding 3, however, is so connected and wound that its magnetic field is in the opposite direc-y compensating .resented by L1+L2+2M12 -and. frequency Vvariation provided by the relative axial movecordance withthe present The total inductance of the winding arrangement illustrated in Figs. 1 and 2 is In this formula Lt represents the total inductance; L1 ,the self inductance of winding I; In the self inductance of winding 2; L: the selfl inductanceof winding 3; M1: themutual inductance of windings I and 2; Mis the mutual inductance of windings I and 3; and Mz: the mutual inductance of windings 2 and 3.

The inductance provided by the concentrically disposed windings I and 2 when considered alone is represented by the terms L1+Lz+2Mu wherein M12 varies in value when the windings I and 2 are moved axially relative to each other. The inductance provided by Athe third winding, 3, is represented by the terms 1a2M132M23 wherein M23 varies in value when the windings 2 and-3 are moved axially relative to each other in the process of tuning bymoving the pair of windings I, 3 and the winding 2` relative to each other.

Referring more particularly to Fig. 3, curves 6 and 1 represent. variation in inductance with linear change in position of the movable or tuning elements, curve 8 represents the varying compensating inductance provided by the third winding 3, and curves 9 and I0 represent variation in frequency, correspondingto the inductance variation, in a circuit (not shown) tuned'by the variable inductance device in accordance with my invention.4 Curve 6 is the characteristic of the inductance variation represented by for example between positions of maximum and minimum inductance. Curve 9 is the corresponding characteristic of the frequency variation repalone. -As shown in the curves 6 and 9 of inductance which are characteristics of the ment of the two concentric windings I and 2 alone, those portions `which are substantially linear are quite short, and the more extended portions wherein the slope varies within permissible limits are also relatively short. To extend the linear portionsof curve 9, or the portions over which the slope varies within permissible limits,

the'third winding 3`is so spaced from winding I andso dimensioned and wound that the term -La--ZMia-2Ma3 represents an inductance varying in a manner to compensate the undue changes curve Sover a considerable portion inductance and frequencyV range.y

in slope in of the total As indicated ,by curve i8 the compensating inductance is preferably positive in the portion of the tuningy range 'toward the maximum inductance end thereof y and becomes negative toward the minimum inductance end, the resultant frequency curve I being thereby. substantially linear over a considerably extended portion of its length as compared Awith the frquency'curve 9. If this 'compensating inductance is increased beyond the requirements for linearity of controlled frequency, the resultant 1 will become substantially inductance curve linear over a considerably extended portion of its length as compared to curve l6.

In a typical variable inductance device in acinvention the windtion in the frequency of ings, arranged as in Fig. 2, were as follows: winding I--98 turns single layer, mean diameter 41/2 inches, length 4/4 inches; winding 2-88 turns single layer, mean diameter 4 inches, length 4 inches; winding 3-11 turns single layer, mean diameter 41/2 inches, length one-half inch. The spacing between the centers of windings I and 3 was 6% inches.

In operation of the above-described typical variable inductance device in tuning a radio circuit over a suitable band of frequencies the frequency characteristics of the device were substantially as illustrated in curve Ii) of Fig. 3, the linear portions, or those portions varying from linearity only by-a permissibly small percentage, being so extended as compared with the similar portions in curve 3 that commercially practical straight line or linear tuning of a circuit was readily accomplished without the necessity of adding mechanical or other compensating means to the tuning control.

My invention has been described herein in a particular embodiment for purposes of illustration. It is to be understood, however, that the invention is susceptible of various changes and modifications and that by the appended claims I intend to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patentof the United States, is:

1. A variable inductance device for use as a variable controlling means for tuning radio and like circuits over a band of frequencies, said device including two windings providing magnetic fields of the same polarity and movable in relation to each other to produce substantially linear variathe controlled circuit over a predetermined portion of the range of said movement, and a third winding in fixed relation with one of said first-named windings and providing a magnetic field of opposite polarity to that of said first-named fields, the total inductance of said device being the sum of the selfinductances of said windings plus the mutual inductance of said two windings and minus the mutual inductances of said third winding taken respectively with each of said two windings, said three windings cooperating to produce substantially linear variation of said frequency over a greater portion of said range.

2. A variable inductance device for use as a variable controlling means for tuning radio and like circuits over bands of frequencies, said device including two concentric windings providing magnetic elds of the same polarity and movable axially in relation to each other to produce a linear variation in the frequency of the controlled circuit over a predetermined portion of the range of said movement, and a third winding spaced axially from and in fixed relation with one of said two windings and providing a magnetic field of opposite polarity to that of said first-named fields, the total inductance of said device being the sum of the self-inductances of said windings plus the mutual inductance of said two windings and minus the mutual inductances of said third winding taken respectively with each of said two windings, said three windings cooperating to produce `linear variation of said frequency over a greater portion of said range.

3. A variable inductance device for use as a variable controlling means for tuning radio and like circuits over bands of frequencies, said device including two windings providing magnetic fields of the same polarity and movable in relation to each other to produce substantially linear variation in the frequency of the controlled circuit over a predetermined portion of the range oi said movement, and a third winding in iixed relation with one of said first-named windings and providing a magnetic ileld of opposite polarity to that ci said ilrst-named fields, the total inductance of said device being the sum of the selfinductances oi said windings plus the mutual inductance oi said two windings and minus the mutual inductances of said third winding taken respectively with each of said two windings, said third winding being so spaced from said one of said iirst-named windings and the eld provided by said third winding being of such value relative to that of the field produced by the other of said first-named windings that said substantially linear variation of said frequency is extended over a greater portion of said range.

4. A variable inductance device for use as a variable controlling means for tuning radio and like circuits over bands of frequencies, said device including two windings providing magnetic fields of the same `polarity and movale in relation to each other to produce substantially linear inductance variation o! said device over a predetermined portion of the range of said movement, and a third winding in ilxed relation with one ot said first-named windings and providing a magnetic ileld of opposite polarity to that of said first-named fields. the total inductance of said device being the sum of the self-inductances ot said windings plus the mutual inductance of said two windings and minus the mutual inductances of said third winding taken respectively with each of said two windings, said three windings cooperating to produce substantially linear variation of said inductance over a greater portion of said range.

5. A variable inductance device for use as a variable controlling means for tuning radio and like circuits 1over bands of frequencies, said device, including two concentric windings providing magnetic ilelds of the same polarity and movable, axially in relation to each other to produce a substantially linear inductance variation of said device over a predetermined portion of the range of said movement, and a third winding spaced axially from and in fixed relation with one of said two windings and providing a magnetic field of opposite polarity to that of said first-named ilelds, the total inductance of said device being the sum of the self-inductances of said windings plus the mutual inductance of said two windings and minus the mutual inductances of said third winding taken respectively with each of said two windings, said three windings cooperating to produce linear variation of said inductance over. a greater portion of said range.

6. A variable inductance device for use as a variable controlling means for tuning radio and like circuits over bands of frequencies. said device including two windings providing magnetic tlelds of the same polarity and movable in relation to each other to produce substantially linear inductance variation of said device over a predetermined portion o! the range of said movement, and a third winding in iixed relation with one of said rst named windings and providing a magnetic field of opposite polarity to that of said mst-named ilelds. the total inductance of said device being the sum oi the selfinductances of said windings plus the mutual inductance of said two windings and minus the mutual inductances of said third winding taken respectively with each of said two windings, said third winding being sofspaced from said one of said first-named windings and the eld provided by said third winding being o1' such value relative to that of the ileld produced by the other of said mst-named windings that said substantially linear variation ot said inductance is extended over a greater portion oi said range. ALBERT O. DODGE.

CERTIFI GATE V GF CORRECTI 0N Y Patent. No'. 2,55l;.,178. November 16, 19145.

ALBERT 0. mDGE.

It ishereby certified that errorappears in the printed ,specification of the ebove numbered patent requiring correction as follows: Page 2, first column', line 5, for'that portion of the formula reading "21125-21125" read 2H152n25; line 20, for "L2n read --L-q and that the sidLettere Patent should te rend with this correction therein that the Seme may conform' to the record of the case in the Patent Office.

Signed andeealed this 1st day of February, A. D. 19h14..

. I Henry Van Arsdnle, (Seal) I A'cting Commissioner of Patents.

CERTIFICATE@ CORRECTION. Percent4 no; 2,551I,178. November 16, 19ML ALBERI o. noma.

It is'hereby certified that errorappeara in the printed Y:specification of the above mxmb'erod patent requiring correction as follows: Page 2, first column', line 5, rorthat portion of the formula reading "2125-2325" read --21115-21'125--3 line 20, for I'L2'I read --L5; and that the sidLotters Patvont should 'be rend with this corrootion therein that the same may coiorml -to the record of the caso in the Patent Office.

signad .nd-sealed this 1st day of February, A. D. 191m.

, i Henry Van Arsdalo, `(Seal) A'cting Commisaioner of Patents. 

